In overhead valve engines, valves are reciprocally mounted in the head and moved toward the cylinder to open. In many such engines, opening movement is imparted by the action of a so-called rocker arm which is a lever mounted intermediate its ends to the head for rocking movement thereon. One end of the rocker arm engages the valve stem, that is, the end of the valve opposite the cylinder, while the other end of the rocker arm is engaged by a pushrod which in turn is operated by the engine cam shaft, typically via a tappet or other valve lifter.
In many engines, the rocker arms are not mounted for movement about a fixed axes. More typically, a semi-spherical bearing is employed and as a consequence, rocker arm movement is not confined to a plane, even though it is highly desirable, as is well known, to confine the rocking movement of the rocker arm about its pivot to a single plane.
To achieve this, the prior art has generally resorted to the use of various types of guide structures. The guides typically are caused to engage the pushrod to confine its movement to reciprocation within the intended rocking plane of the rocker arm. Thus, in U.S. Pat. No. 4,856,467, issued Aug. 15, 1989, to Kronich, there is disclosed a guide plate which is anchored to the head of the engine via a nut on the rocker arm stud. The mounting plate includes spaced, parallel, coplanar guide surfaces which engage the pushrod on opposite sides intermediate its ends.
Because it is desirable to minimize the mass of the pushrod, while at the same time maximize the size of bearing surfaces at the ends of the pushrods to minimize the stresses thereat, many pushrods have enlarged ends and are relatively narrow intermediate their ends. Thus, in the Kronich patent, it is necessary to provide enlarged holes in the guide plate adjacent the ends of the guide surfaces so as to allow insertion of the enlarged end of the pushrods through the guide plate during pushrod installation.
This type of structure, while performing its intended function of guiding the pushrods, has a number of disadvantages. For one, the guide scheme is relatively complex in terms of intricacies of the pushrod receiving apertures in the guide plate and the need to provide opposed guiding surfaces and as well as an enlarged opening to facilitate installation. For another, the placing of the guide plate against the head of the engine to be held in place by the rocker arm stud may, in some instances, undesirably increase the height of the valve train proportional to the thickness of the guide plate.
For still another, because the guide surfaces are coplanar, wear will be occurring at the same location on diametrically opposite sides of the pushrod thereby reducing its life at an accelerated rate as, for example, compared to a guide system that causes wear on a pushrod only on one side thereof at any given point intermediate its ends.
The present invention is directed to overcoming one or more of the above problems.